supplementary materials

N,N'-(4,5-Dimethyl-1,2-phenylene)bis(pyridine-2-carboxamide)

In the title compound, C20H18N4O2, the dihedral angles between the central benzene ring and the pyridine rings are 57.55 (6) and 22.05 (8)°. The molecular conformation is stabilized by intramolecular N-HN interactions and in the crystal structure an intermolecular asymmetric cyclic hydrogen-bonding association involving both amide N-H donors and a common amide O-atom acceptor gives a chain extending along the c axis.

The title compound C20H18N4O2 was synthesized as a ligand for potential
use in medical and radiopharmaceutical applications. In this compound, which
has one molecule in the asymmetric unit (Fig. 1), the dihedral angles between
the central benzene ring and the pyridine rings are 57.55 (6) and 22.05 (8)°.
The molecular conformation is stabilized by intramolecular N—H···N
interactions and in the crystal structure an intermolecular asymmetric cyclic
hydrogen-bonding association involving both amide N—H donors and a common
amide O-atom acceptor (O2i) (Table 1), give a one-dimensional chain
extending along c. The related structures from Roodt et al.
(2011) and Schutte et al. (2011) also contribute to our
studies in
radiopharmaceutical design and reactivity.

Under oxygen atmosphere, picolinic acid (5.73 g, 0.0465 mol) was added as a
solid in one portion to a suspension of 4,5-dimethyl-1,2-phenylenediamine
(3.00 g, 0.0220 mol) in pyridine (20 ml) and the mixture was stirred at 40 °C
for 40 min. Triphenylphosphite (30 ml) was added dropwise over 10 minutes
after which the temperature was increased to 90–100 °C and stirred for a
further 24 h. On cooling the precipitate was filtered, washed with H2O (50 ml) and then MeOH (50 ml). The precipitate was recrystallized in chloroform to
giving colourless crystals after five days

Experimental. The intensity data was collected on a Bruker X8 ApexII 4 K Kappa CCD
diffractometer using an exposure time of 30 s/frame. A total of 1895 frames
was collected with a frame width of 0.5° covering up to θ = 28.29° with
99.9% completeness accomplished.

Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are
estimated using the full covariance matrix. The cell s.u.'s are taken into
account individually in the estimation of s.u.'s in distances, angles and
torsion angles; correlations between s.u.'s in cell parameters are only used
when they are defined by crystal symmetry. An approximate (isotropic)
treatment of cell s.u.'s is used for estimating s.u.'s involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor
wR and goodness of fit S are based on F2, conventional
R-factors R are based on F, with F set to zero for
negative F2. The threshold expression of F2 >
2σ(F2) is used only for calculating R-factors(gt) etc.
and is not relevant to the choice of reflections for refinement.
R-factors based on F2 are statistically about twice as large
as those based on F, and R- factors based on ALL data will be
even larger.